[ Upstream commit 41be3e2618174fdf3361e49e64f2bf530f40c6b0 ]
vfio_dev_present() which is the condition to wait_event_interruptible_timeout(), will call vfio_group_get_device and try to acquire the mutex group->device_lock.
wait_event_interruptible_timeout() will set the state of the current task to TASK_INTERRUPTIBLE, before doing the condition check. This means that we will try to acquire the mutex while already in a sleeping state. The scheduler warns us by giving the following warning:
[ 4050.264464] ------------[ cut here ]------------ [ 4050.264508] do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000b33c00e2>] prepare_to_wait_event+0x14a/0x188 [ 4050.264529] WARNING: CPU: 12 PID: 35924 at kernel/sched/core.c:6112 __might_sleep+0x76/0x90 ....
4050.264756] Call Trace: [ 4050.264765] ([<000000000017bbaa>] __might_sleep+0x72/0x90) [ 4050.264774] [<0000000000b97edc>] __mutex_lock+0x44/0x8c0 [ 4050.264782] [<0000000000b9878a>] mutex_lock_nested+0x32/0x40 [ 4050.264793] [<000003ff800d7abe>] vfio_group_get_device+0x36/0xa8 [vfio] [ 4050.264803] [<000003ff800d87c0>] vfio_del_group_dev+0x238/0x378 [vfio] [ 4050.264813] [<000003ff8015f67c>] mdev_remove+0x3c/0x68 [mdev] [ 4050.264825] [<00000000008e01b0>] device_release_driver_internal+0x168/0x268 [ 4050.264834] [<00000000008de692>] bus_remove_device+0x162/0x190 [ 4050.264843] [<00000000008daf42>] device_del+0x1e2/0x368 [ 4050.264851] [<00000000008db12c>] device_unregister+0x64/0x88 [ 4050.264862] [<000003ff8015ed84>] mdev_device_remove+0xec/0x130 [mdev] [ 4050.264872] [<000003ff8015f074>] remove_store+0x6c/0xa8 [mdev] [ 4050.264881] [<000000000046f494>] kernfs_fop_write+0x14c/0x1f8 [ 4050.264890] [<00000000003c1530>] __vfs_write+0x38/0x1a8 [ 4050.264899] [<00000000003c187c>] vfs_write+0xb4/0x198 [ 4050.264908] [<00000000003c1af2>] ksys_write+0x5a/0xb0 [ 4050.264916] [<0000000000b9e270>] system_call+0xdc/0x2d8 [ 4050.264925] 4 locks held by sh/35924: [ 4050.264933] #0: 000000001ef90325 (sb_writers#4){.+.+}, at: vfs_write+0x9e/0x198 [ 4050.264948] #1: 000000005c1ab0b3 (&of->mutex){+.+.}, at: kernfs_fop_write+0x1cc/0x1f8 [ 4050.264963] #2: 0000000034831ab8 (kn->count#297){++++}, at: kernfs_remove_self+0x12e/0x150 [ 4050.264979] #3: 00000000e152484f (&dev->mutex){....}, at: device_release_driver_internal+0x5c/0x268 [ 4050.264993] Last Breaking-Event-Address: [ 4050.265002] [<000000000017bbaa>] __might_sleep+0x72/0x90 [ 4050.265010] irq event stamp: 7039 [ 4050.265020] hardirqs last enabled at (7047): [<00000000001cee7a>] console_unlock+0x6d2/0x740 [ 4050.265029] hardirqs last disabled at (7054): [<00000000001ce87e>] console_unlock+0xd6/0x740 [ 4050.265040] softirqs last enabled at (6416): [<0000000000b8fe26>] __udelay+0xb6/0x100 [ 4050.265049] softirqs last disabled at (6415): [<0000000000b8fe06>] __udelay+0x96/0x100 [ 4050.265057] ---[ end trace d04a07d39d99a9f9 ]---
Let's fix this as described in the article https://lwn.net/Articles/628628/.
Signed-off-by: Farhan Ali alifm@linux.ibm.com [remove now redundant vfio_dev_present()] Signed-off-by: Alex Williamson alex.williamson@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/vfio/vfio.c | 30 ++++++++++-------------------- 1 file changed, 10 insertions(+), 20 deletions(-)
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c index f5a86f651f38..0d73d913c18b 100644 --- a/drivers/vfio/vfio.c +++ b/drivers/vfio/vfio.c @@ -34,6 +34,7 @@ #include <linux/uaccess.h> #include <linux/vfio.h> #include <linux/wait.h> +#include <linux/sched/signal.h>
#define DRIVER_VERSION "0.3" #define DRIVER_AUTHOR "Alex Williamson alex.williamson@redhat.com" @@ -909,30 +910,17 @@ void *vfio_device_data(struct vfio_device *device) } EXPORT_SYMBOL_GPL(vfio_device_data);
-/* Given a referenced group, check if it contains the device */ -static bool vfio_dev_present(struct vfio_group *group, struct device *dev) -{ - struct vfio_device *device; - - device = vfio_group_get_device(group, dev); - if (!device) - return false; - - vfio_device_put(device); - return true; -} - /* * Decrement the device reference count and wait for the device to be * removed. Open file descriptors for the device... */ void *vfio_del_group_dev(struct device *dev) { + DEFINE_WAIT_FUNC(wait, woken_wake_function); struct vfio_device *device = dev_get_drvdata(dev); struct vfio_group *group = device->group; void *device_data = device->device_data; struct vfio_unbound_dev *unbound; unsigned int i = 0; - long ret; bool interrupted = false;
/* @@ -969,6 +957,8 @@ void *vfio_del_group_dev(struct device *dev) * interval with counter to allow the driver to take escalating * measures to release the device if it has the ability to do so. */ + add_wait_queue(&vfio.release_q, &wait); + do { device = vfio_group_get_device(group, dev); if (!device) @@ -980,12 +970,10 @@ void *vfio_del_group_dev(struct device *dev) vfio_device_put(device);
if (interrupted) { - ret = wait_event_timeout(vfio.release_q, - !vfio_dev_present(group, dev), HZ * 10); + wait_woken(&wait, TASK_UNINTERRUPTIBLE, HZ * 10); } else { - ret = wait_event_interruptible_timeout(vfio.release_q, - !vfio_dev_present(group, dev), HZ * 10); - if (ret == -ERESTARTSYS) { + wait_woken(&wait, TASK_INTERRUPTIBLE, HZ * 10); + if (signal_pending(current)) { interrupted = true; dev_warn(dev, "Device is currently in use, task" @@ -994,8 +982,10 @@ void *vfio_del_group_dev(struct device *dev) current->comm, task_pid_nr(current)); } } - } while (ret <= 0);
+ } while (1); + + remove_wait_queue(&vfio.release_q, &wait); /* * In order to support multiple devices per group, devices can be * plucked from the group while other devices in the group are still